1. Field of the Invention
The present invention relates to a disk drive apparatus having a head loading/unloading control system and a method for controlling head loading/unloading operations in the apparatus. More particularly, it relates to an apparatus and a method for performing reliable head loading/unloading operations even when a shutdown of a primary power source occurs during the operation of the disk drive apparatus.
2. Description of the Related Art
Conventionally, a magnetic disk drive apparatus, such as a hard disk drive apparatus, (hereinafter simply referred to as a “disk drive”) is used for writing and/or reading data on and from a data recording disk medium (hereinafter referred to as a “disk”) by loading magnetic head elements onto a target track in the disk when the rotation speed of the disk reaches a steady state. A spindle motor (SPM) rotates the disk. The head loading and/or unloading operations are controlled by a central processing unit (CPU) installed in the apparatus.
The writing/reading head elements are initially rested upon a rest position. During the writing/reading operations, the head elements are loaded from the rest position so as to float closely above a surface of the disk when the rotation speed of the disk reaches a steady state in order to avoid possible damage of data areas in the disk due to contact between a head surface and a disk surface.
In order to prevent the head surface from contacting the rotating disk surface during the head drive operations, usually, the disk drive applies a contact-start-stop (CSS) system or a loading/unloading system. In the CSS system, the head elements are placed on a retract zone (CSS area) in the disk when the disk is in a non-rotation state. Conventionally, the disk drive of the CSS system includes a ring shaped CSS area at an inner side of the data zone of the disk. In the disk drive of the head loading/unloading system, the head elements are retracted (unloaded) onto a rest unit (hereinafter, simply referred to as a “ramp unit”) provided at near the outer edge of the disk during when the disk is in a non-rotation state. In both systems, the head elements are moved by the rotation of a voice coil motor (VCM). A VCM drive circuit supplies VCM drive currents in order to rotate the VCM.
In order to increase the data recording density of the disk, the head surface is floated very closely to the disk surface. Thus, the data recording density of the disk can be increased by reducing the head floating height. However, the damages due to contact of the head surface with the disk surface also increases when the head floating power is reduced. Thus, if a shutdown of the primary power source for the apparatus occurs during the operations of the disk drive, the head surface will likely contact the disk surface due to the inertia rotation of the spindle motor (SPM). In order to avoid this defect in the disk drive, it needs to retract the head elements to the CSS area or the ramp unit before stopping the spindle motor (SPM). However, since the primary power source has already shutdown, there is a need to supply the VCM drive current in order to move the head elements to the rest position from a reserve power source.
Conventionally, it has been proposed to perform a stabilized head retracting operation at the time of a sudden shutdown of the primary power source. For example, Japanese Patent Application No. 2000-21073 (the same assignee of this invention) has proposed to acquire data for controlling the head retraction based on a head position in a determination process during a normal operation of the disk drive. Thus, in order to immediately perform the head retracting operation at a shutdown time of the power source with a lower electric power, the data for controlling a head retraction is periodically acquired during a normal head driving control time. When a shutdown of the primary power source occurs, the head elements are moved to a retraction place by driving through an auxiliary power supply. As the auxiliary power supply, a condenser or the back electromotive voltages of the SPM are proposed.
The proposed head retracting operation by using the auxiliary power supply, however, includes some defects. For example, if the primary power source is shut down immediately after the disk drive is operated, it is impossible to charge a sufficient battery voltage in the condenser or to obtain a sufficient auxiliary power, by rectifying the back electromotive force of the inertia rotation of the SPM, for retracting the head elements.
Moreover, there is a possibility to have a failure of the condenser even after a shutdown of the primary power source has occurred. If the primary power source has shutdown in such a state, it is impossible to retract the head elements to the rest position.